Relaxed magnetohydrodynamics with cross-field flow

TL;DR

This paper extends the phase-space Lagrangian model of Dewar et al. to include cross-field flows in relaxed MHD equilibria, analyzing their effects across different geometries and linking flow to magnetic island structures.

Contribution

It characterizes the steady-state solution space, derives a solvability condition coupling flow and geometry, and constructs equilibria in various geometries with flow effects on magnetic islands.

Findings

Flow strongly correlates with magnetic-island structure in toroidal geometry.

Varying rotation frequency modifies the dominant harmonic of magnetic fields.

Flow parameters influence equilibrium profiles more than island width.

Abstract

The phase-space Lagrangian model of Dewar et al. (Phys. Plasmas 27, 062507, 2020) provides a framework for incorporating cross-field flow into relaxed equilibria while retaining ideal magnetohydrodynamics force balance. Here, we characterize the steady-state solution space and identify a solvability condition that couples the prescribed constrained flow to the geometry through the metric tensor. Using this condition, we construct equilibria in slab, cylindrical, and toroidal geometries. In toroidal geometry, the cross-field flow strongly correlates with magnetic-island structure: varying the rotation frequency modifies the dominant Fourier harmonic of the radial component of the magnetic field and can drive a transition from a primary (m = 1) island to secondary (m = 2) islands. In slab and cylindrical geometries, flow parameters weakly affect island width but strongly modify equilibrium profiles.